This invention relates to switch assemblies and, in particular, to switch assemblies utilized in conjunction with conventional centrifugal actuators in dynamoelectric machines.
A variety of dynamoelectric machines, for example, capacitor start and split phase induction motors, utilize a first winding combination for the starting condition of motor operation, and a second winding combination for the run condition of motor operation. These motors commonly include a stator assembly having a central, axially extending bore opening and a rotor assembly mounted for rotation with respect to the stator assembly, carried in the bore opening. The stator assembly includes a core constructed from a plurality of individual laminations formed from a suitable magnetic material. Each lamination, in addition to the bore opening, has a plurality of radially extending slots opening onto the bore along one end of the slots. The motor winding conventionally is disposed in the aligned slots of the lamination plurality in some predetermined manner.
As indicated, the bore opening is intended to receive the rotor assembly. The rotor assembly preferably includes a squirrel cage rotor, for example, and a shaft mounted for rotation along suitable bearing means conventionally housed in each one of a pair of end shields. The end shields commonly either are attached to the stator assembly, or to a shell enclosing the stator assembly. A centrifugal actuator usually is mounted to the shaft and rotates with it. The centrifugal actuator is intended to engage a switch arm which in turn operates a switch mechanism for connecting or disconnecting a source of electrical energy to various motor winding circuit configurations as motor speed varies. In the split phase motor illustratively discussed above, it is conventional to remove an auxiliary or start winding from the motor electrical circuit as the motor nears running speed. After removal of the start winding, the motor operates on a run or main winding unless motor speed decreases to the point where the actuator re-engages the switch arm to connect the start winding back into the motor circuit.
A number of switch assemblies are known in the prior art. One prevalent design includes a switch and switch enclosure which is mounted externally of the motor. For example, the switch assembly usually is mounted to one of the motor end shields. This particular design has a separate switch arm placed through the end shield which engages the centrifugal actuator in at least one of the actuator positions. While these prior art devices work well for their intended purposes, they generally are characterized by expensive construction techniques. For example, in the prevalent design described, means for mounting the switch assembly to the end shield is required. Means for inserting the switch arm through the end shield also is necessary. In addition, because the switch assembly is mounted on the outside of the motor enclosure, the various motor leads are exposed both to environmental conditions and unauthorized personnel.
Switch assemblies which are mounted internally of the end shields also are known in the art. As a class, they generally are relatively expensive if desirable features, such as lost motion movement later described, is provided.
Our invention eliminates these prior art deficiencies in that a simple, low cost device is provided which may be mounted internally of the motor end shields. The device functions both as a terminal board connection device and a switch assembly. Switch assembly operation is controlled by a conventional centrifugal actuator. Access to the terminal board may be made through the end shield after removal of a common, low cost cover plate. The switch assembly construction is designed to provide lost motion movement in at least one direction of switch assembly operation. The provision of lost motion movement means that false engagement of the various connections made through the switch assembly may be eliminated or reduced with out switch design. In addition, contact pressure in conventional switch designs often is dependent on the position of the switch arm. If the switch arm for some reason does not clear the centrifugal actuator during operation, the contact pressure is reduced or non-existent. Reduced contact pressure, in turn, can have adverse affects on motor life. Our design eliminates the interrelation of contact pressure and switch arm position prevalent in prior art switch assembly designs. The switch assembly of our invention includes at least one movable arm which is pre-shaped so as to bias the arm, and its associated contact point, into engagement with a fixed contact carried by a non-movable portion of the switch assembly.
One of the objects of this invention is to provide a low cost switch device for a dynamoelectric machine.
Another object of this invention is to provide a switch assembly having contact pressure independent of switch arm position.
Another object of this invention is to provide a switch assembly which may be mounted internally of the motor end shield.
Another object of this invention is to provide a switch assembly which is integrally formed with a terminal board structure.
Another object of this invention is to provide a simplified switch structure.
Other objects of this invention will be apparent to those skilled in the art in light of the following description and accompanying drawings.